The Nissan Club banner
1 - 15 of 15 Posts

·
Man with Car
Joined
·
228 Posts
Discussion Starter · #1 · (Edited)
I'm a new guy here, so forgive me if I overstep my bounds. But something is fishy about the first round of dynomometer numbers recently posted, and since nobody seemed to pick up the ball and run with it, I figured I'd better dive on the thing.

First, a recap: Greg Vogel at Mossy Nissan has stepped up to the plate with the first cat-back exhaust system for the '02 3.5SE. I think it's darned impressive that anyone with such limited resources could develop and produce a nice-looking exhaust like this one. (The mufflers are too ricey for me, but otherwise the thing looks well screwed together.)

A short time after announcing the system was for sale, Mr. Vogel took an automatic 3.5SE to a local dyno shop and ran the thing with the stock exhaust in place and with his aftermarket unit bolted on. He came up with the following wheel horsepower numbers:

Stock HP peak: 164, no rpm given
Mossy HP peak: 179, no rpm given

Mr. Vogel also ran a 3.5SE with a JWT POPCharger on a dynomometer. He didn't indicate whether this was the same car, the same dynomometer, or even the same day, but he posted the following numbers:

Stock HP peak: 164, no rpm given
POPCharger peak: 174, no rpm given


So what we're looking at is an *extremely* impressive 15 peak horsepower improvement over stock with the Mossy exhaust (and he indicates as many as 20 more horsepower elsewhere on the power curve) and a *very* dynamic 10 horsepower peak gain with the JWT intake. And what we're also seeing is a mathematical quandary of sorts. Nissan advertises 240 SAE crank horsepower for the VQ as installed in this Altima. Including a very conservative number for driveline loss to the front wheels of 20 percent, we should be looking at approximately 192 horsepower on the rollers. Instead, Mr. Vogel reports he's seeing 164, which if the VQ in his test car is making the full complement of 240 horses to the crank indicates a power-sapping driveline loss of 32 percent. Considering the efficiency of today's FWD transaxles, this number flatly does not compute. (In the SE-R community of which I was a member for quite some time, the standard observed driveline loss was in the 15 to 18 percent range.)

So the question is this: Where did all the horses go? Who left the barn door open? Considering the widely tested and reported acceleration numbers for this 3000-pound car, 164 wheel horsepower just ain't gonna get it done. Low- to mid-seven second sprints to 60 miles an hour in SEs with automatic transmissions cannot occur with such low wheel horsepower numbers. And we can certainly be sure that the mid-90 mph trap speeds would be impossible with so much weight and so few horses.

Greg, I'm thinking that your test car is sick. That's the only explanation. I'm also a little leery of those massive horsepower gains you posted. I *really* doubt that the stock exhaust system aft of the catalytic converters is so horribly restrictive that you can free up 15 to 20 horses just by bolting on your exhaust. Heck, 20 wheel horsepower would be an impressive achievement for a full-on set of headers *combined* with a free-flowing exhaust -- we're talking about opening up 25 horsepower at the crank! And the same goes for 10 horses you discovered with the JWT. Bolting on a conical filter and finding twelve or thirteen additional flywheel horsepower is nearly unheard of with relatively small Japanese engines.

Greg, I know that Mossy Nissan doesn't have unlimited pockets for R&D in your parts department, but I'd advise you to run at least two or three other 3.5s -- a mixture of automatics and manuals, if possible -- on the dyno before jumping to the conclusion that these simple bolt-on mods produce such a dramatic horsepower improvement. The sick-looking stock wheel horsepower numbers your test Altima posted should be proof enough of the need for that. (And folks, mods of this type do not produce cumulative horsepower; that is, bolting on both the JWT and the exhaust won't net you a gain of 30 horsepower to the wheels and 38 or so at the crank. Ain't gonna happen. You will not have a 278-horsepower Altima.)

Again, please don't take any of this personally. I'm no engineer. But I do know that when it sounds too good to be true, it very often is.

Jarrod K. Wright
'02 3.5SE 5-speed
'98 SE 5-speed
 

·
Registered
Joined
·
1,323 Posts
greg, i suggest u follow the advice of the SER guys and take the car to R&D @ the next meet. I totally back u up and believe that the dyno u used was not up to standards. Don't waste your time or $ dynoing other cars @ the same place just to satisfy us. U know your sentra does more hp than what u got, so we know the dyno's not as good as it should be.
I got your back on this one. Thanx for all the hard work.
Jay
 

·
Registered
Joined
·
6 Posts
Relax, you mentioned that Greg V. tested an automatic altima, so a 32% drivetrain loss is about the average.( I had a celica GT-S, dyno'd at 140 wheel HP.) Now a manual transmission on the other hand is different; I'm gonna dyno my 5 speed Alty and I'll post the results.
 

·
Man with Car
Joined
·
228 Posts
Discussion Starter · #9 ·
geoffrey said:
Relax, you mentioned that Greg V. tested an automatic altima, so a 32% drivetrain loss is about the average.
Ah, no, it's not. While automatic transmissions are not as efficient as manual transmissions, they *do not* sap a third of a car's crank horsepower. Healthy automatic Corvettes do not dyno at 234 rear-wheel horsepower; automatic V8 Camaros do not dyno at 207 RWH. Were either of these the case, we'd see the line of GM powertrain engineers at the unemployment office stretch around the block. (I haven't actually verified the latter myself, so if there is such a line in Michigan somewhere, I'll assume it's for other reasons.) ;)

Another issue that I didn't delve into for lack of expertise is the dynomometer itself. Was it running properly? Is it calibrated correctly? I know it wasn't a Dynojet, by far the most universal and trusted brand of chassis dynomometer; does that have any bearing on the results?

There are a ton of variables here that should be analyzed. Simply accepting both the low horsepower figures and the extraordinarily large gains produced by these simple bolt-ons (and I'm much more skeptical of the latter) seems foolhardy. I know I'd like a heckuva lot more data before forking over $700 for an exhaust system whose efficacy can, and should, be questioned for lack of testing. And again, this isn't a a shot at Mr. Vogel or Mossy Nissan, a company in business to sell cars, not manufacture exhaust systems. Expectations must be adjusted based on this.

Jarrod K. Wright
'02 3.5SE 5-speed
'98 Altima SE
 

·
Registered
Joined
·
13 Posts
It is starting to seem like in this case, the low hp numbers was a result of the auto tranny (directly or indirectly). Apparantely the runs were done while the car was in 2nd gear...no 1:1 ratio...torque converter never locked up? What do you think?
 

·
Registered
Joined
·
2 Posts
jkwright is absolutely right. I can vouch for the Corvette, Camaro and Transam LS1 quotes on drive train loss. The typical drivetrain loss on a MN6 (6 - speed) Y or F-body is about 15% HP loss to the rear wheels and an A4 (automatic) has about an 18% HP loss to the rear wheels. The 32% parasitic HP loss to the wheels on a front wheel drive car is absurd. With today's cars that isn't plausible. Front wheel drive has less distance to transfer the power to the wheels so they should(usually) have even less of a HP loss to the front (drive) wheels.

Something isn't adding up. Dyno results are always something to consider but usually you take them with a grain of salt. The Dyno could have not been setup correctly, not lubricated correctly among other things. However, at least it was a Dynometer one. The Mustang Dynos are notorious for putting out higher numbers.

To do a dyno run you must do it in the respective gear ratio that provides a 1:1 response. In my case that'd be in 4-th gear. Anyone know the 1:1 ratio for the automatics? The track is most always the best determinant of performance gains :D, especially with the consistency of an automatic :D.
But that exhaust is BAD ASS looking! Any sound clips on it?
 

·
Registered
Joined
·
1,323 Posts
does anybody know when the tc is supposed to lock up? I heard some of the nicer cars like Lexus's lock up in 2nd.
Jay
 

·
X-Mod
Joined
·
1,585 Posts
They only lock up in overdrive (as far as I know) to eliminate the small percentage of slippage always present in a hydraulic torque converter. Conserves fuel and reduces heat buildup in the trans. I guess newer cars could lock up their TQ's in second or third at steady speeds but I never heard of this. Anyone know? I would think not because an auto should shift to overdrive at any steady cruise speed above 40-45mph, and only then lock up.
 

·
Man with Car
Joined
·
228 Posts
Discussion Starter · #15 ·
super_black said:
It is starting to seem like in this case, the low hp numbers was a result of the auto tranny (directly or indirectly).
I really don't think so, Super. And the more I think about it, the more I doubt that the Altima Greg dynoed was so sick it was short 40 horsepower at the crank. An engine in that condition would surely be noticeable to the butt-o-meter, and since Greg seems to be a performance guy, I presume his ass is, uh... fairly sensitive. ;)

I believe the problem is with either the test methodology or the dynomometer itself. However...

..torque converter never locked up? What do you think?
If the torque converter indeed hadn't locked up and some viscous slippage was occurring during the run, then yes, that'd sap some ponies. But 40 at the crank and 32 at the wheels? I dunno. NastyC5, how much experience do you have with automatic Corvettes and dynos? Any thoughts on this?

Jarrod K. Wright
'02 3.5SE 5-speed
'98 SE 5-speed

PS - Were I a) unmarried and b) made of money, I'd have a nasty black Corvette in the garage and a million super-soft Chamois to keep it swirl-free. ;)
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top